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According to the literature4•6 the highest oxide of sodium that can be obtained by combustion of the metal in an excess of oxygen is the peroxide, Na2C>2. The superoxides of potassium, rubidium and cesium may be prepared by the same method.6•6 Although previous investigators7 have studied the reaction between alkaline earth metal lower oxides with oxygen at elevated temperatures and pressures in attempts to prepare higher oxides, no similar experiments have been performed with sodium peroxide. Holt and Sims5 passed oxygen at atmospheric pressure over sodium peroxide at 300-350°for sixteen hours but obtained no evidence of oxygen absorption. In a previous report8 from this Laboratory, dealing with the rapid oxidation of sodium in liquid ammonia, evidence for the existence of sodium superoxide was described.9 In the present investigation sodium peroxide has been subjected to treatment with oxygen at high pressures and temperatures in order to explore the possibility of preparing higher oxides by this method. Such treatment results in the formation of high yields of sodium superoxide. The preparation and magnetic properties of this substance are discussed in this paper.

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Studies of the NH< +-H + and Ag +-H + exchanges on Dowex 50 at 25°in solutions of unit ionic strength have shown that the equilibrium composition of solid and liquid phases is determined by (a) the extent of simple equivalent ion exchange, which may be regarded as a chemical reaction, (b) the absorption or desorption of water by the resin, (c) the adsorption of electrolyte by the resin, and (d) the apparent molal volume change of the solute. Water absorption is a linear function of resin composition, but electrolyte adsorption depends in a more involved fashion on both resin and solution composition. New data for the Na+-H + exchange on Dowex 50 in solutions of ionic strength 1.0 and 0.3 M have been combined with solution activity coefficient ratios from the literature to obtain, by a method of graphical integration, the activity coefficients of the resin components and the true exchange equilibrium constant. The activity coefficients, less than unity, agree well for the two ionic strengths. The value of the equilibrium constant at 25°is 1.70 ± 0.03.